I. Field of the Invention
The present invention relates to a system and method for determining the radiological features of a very low area density sample using an imaging system and a source of low energy x-ray emission. Area density is the amount of sample mass (such as grams) through which the x-ray beam passes, per unit area (cm.sup.2) of the beam diameter. Area density is the product of the usual sample volume density (g/cm.sup.3) times the path length of sample (cm) along the beam.
II. Description of the Prior Art
There are many previously known x-ray inspection systems for producing images of one sort or another. For example, medical systems using hard or high energy x-rays have long been used to produce images of bones and the like. Such high energy x-rays pass with little attenuation through air and are suitable for imaging very dense and/or very thick objects.
Conversely, soft x-rays, i.e. x-rays having an energy of less than 3 kilovolts, are rarely used in industrial inspection applications. Soft x-rays, however, attenuate rapidly as they pass through air. As such, such industrial applications utilizing soft x-rays must necessarily retain the sample under inspection within a vacuum or non-absorbing atmosphere such as helium in order to prevent excessive attenuation of the soft x-rays.
None of the previously known systems, however, have utilized low energy or border x-rays, i.e. x-rays having an energy level in the range of 3 kilovolts to 15 kilovolts and thus in between soft x-rays and hard x-rays.